What’s a good chip for gas mileage and performance ?

 

There's no "chip". What you're after is a computer tune.

Easiest option is a plug in tuner. Designed specifically for the vehicle, plugs into the OBD port under the dash, displays a few prompts on the device and lets you pick a few option, then flashes changes to the computer.

The BEST option is to actually have it tuned by a local shop. They can go as far as running it on a dyno and getting the most out of it, but it's going to cost much more...